The finding of high antitumor activity of 9-aminocamptothecin (9- AC) suggests the preparation of a number of other 9-substituted compounds which we have reason to believe will have high activity in L1210 mouse leukemia. These include the 9-cyano, 9,10-methylene dioxy, and 9-hydroxy analogs. In order to extend the clinical applicability of our most active camptothecin compounds which are water insoluble, we propose to prepare water soluble analogs which in many cases would be acting as pro- drugs for the parent compound, such as the 21-glycinate esters of 9- or 10-AC, certain water soluble esters of 9- or 10- hydroxy-1a or water soluble amides of 9- or 10 AC. Whether the pyridine nitrogen in ring B and the pyridone moiety in ring D are required for activity will be ascertained by synthesis of analogs 1b and 2, which have the same shape and size of camptothecin. An analog with much different shape such as 3 will also be prepared and tested in vitro and in vivo. A major study will be conducted to ascertain whether the same structural requirements for in vivo antitumor activity of 1a apply also to the interference of 1a with topoisomerase (Topo I) function in biochemical systems and to determine whether drug action on Topo I is responsible for the observed antitumor activity. In this connection, the mechanism of inhibition of Topo I by 1a and analogs, the production of protein-associated strand breaks with selected key 1a analogs, and the sites of drug-induced trapping of DNA-Topo I cleavage complexes to the genome will be studied. These studies will be facilitated by the preparation of radiolabeled camptothecin and one or two key analogs.